Weight-related ailments such as diabetes and heart disease are growing problems in developing countries. But such diseases are affecting mostly the rich. For the most part, according to a Harvard School of Public Health (HSPH) study, the poor in developing nations are still thin and often undernourished.

In lower-income nations there is a large social divide when it comes to “first-world” diseases, according to the study’s senior author, HSPH Professor of Population and Health and Geography S V Subramanian. “On average, people are getting heavier in these countries,” Subramanian told Reuters. “But who is getting heavier?”

Because of the disparity, Subramanian said, many countries need to promote two opposite public health efforts: one to encourage the wealthy to cut calories, and one to get more food to the poor.

Subramanian conducted the study, which appeared in the November 2011 American Journal of Clinical Nutrition, with colleagues from HSPH and Bristol University in the United Kingdom. The researchers looked at body mass index (BMI) among more than 547,000 women from 37 low- and middle-income countries in Asia, Africa, and South America.